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Rev. 1.00
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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
Oscillators
Various oscillator options offer the user a wide range of functions according to their various
application requirements. The flexible features of the oscillator functions ensure that the best
optimisation can be achieved in terms of speed and power saving. Oscillator selections and operation
are selected through relevant control registers.
Oscillator Overview
In addition to being the source of the main system clock the oscillators also provide clock sources
for the Watchdog Timer and Time Base Interrupts.
F
ully integrated internal oscillators, requiring no
external components, are provided for fast system oscillator and other low frequency requirements.
The higher frequency oscillator provide
s
higher performance but carry with it the disadvantage of
higher power requirements, while the opposite is of course true for the lower frequency oscillator.
With the capability of dynamically switching between different system clock
s
, the device ha
s
the
flexibility to optimize the performance/power ratio, a feature especially important in power sensitive
portable applications.
Type
Name
Frequency
Internal High Speed RC
HIRC
16MHz
Internal Low Speed RC
LIRC
3�kHz
Oscillator Types
System Clock Configurations
There are two oscillator sources, one high speed oscillator and one low speed oscillator. The high
speed system clocks
is
sourced from the internal 16
MHz
RC oscillator, HIRC. The low speed
oscillator
is
the internal 32kHz RC oscillator, LIRC. Note that the system clock only comes from
HIRC. Selecting whether the f
H
or f
H
/2~f
H
/64 clock is used as the system clock is implemented
using the HLCLK bit and CKS2~CKS0 bits in the SMOD register and as the system clock can be
dynamically selected. Note that two oscillator selections must be made namely one high speed and
one low speed system oscillators. It is not possible to choose a no-oscillator selection for either the
high or low speed oscillator.
High Speed
Oscillator
6-stage
Prescaler
HLCLK�
CKS�~CKS0 bits
f
H
f
H
/�
f
H
/4
f
H
/�
f
H
/16
f
H
/3�
f
H
/64
f
SYS
HIRC
System Clock Configurations